Abstract:

The life of an image display apparatus is lengthened while suppressing
luminance unevenness and cross-talk on the screen. To achieve the object,
an image display apparatus includes a light-emitting device of which
emission luminance varies with the amount of current, a first
transistorin which the amount of current between a first electrode
electrically connected to the light-emitting device and a second
electrode is adjusted by the potential applied to a third electrode, so
as to control the amount of current in the light-emitting device, a
second transistor in which the amount of current between a fourth
electrode electrically connected to the first electrode and a fifth
electrode electrically connected to the third electrode is adjusted by
the potential applied to a sixth electrode, and a capacitor having a
seventh electrode electrically connected to the third electrode and an
eighth electrode. A parasitic capacitance between the fifth electrode and
the sixth electrode is set at a larger value than a parasitic capacitance
between the fourth electrode and the sixth electrode.

Claims:

1-13. (canceled)

14. An image display apparatus comprising:a light-emitting device of which
emission luminance varies with the amount of current;a first transistor
having first electrode, second electrode and third electrode, wherein the
amount of current between the first electrode and the second electrode is
adjusted by a potential applied to the third electrode;a second
transistor having fourth electrode, fifth electrode and sixth electrode,
wherein the amount of current between the fourth electrode and the fifth
electrode is adjusted by a potential applied to the sixth electrode; anda
capacitor having seventh electrode and eighth electrode and forming a
capacitance between the seventh electrode and the eighth electrode,the
first electrode being electrically connected to the light-emitting
device, wherein the amount of current in the light-emitting device is
controlled by adjusting the amount of current between the first electrode
and the second electrode,the fourth electrode being electrically
connected to the first electrode, the fifth electrode being electrically
connected to the third electrode,the seventh electrode being electrically
connected to the third electrode,a parasitic capacitance between the
fifth electrode and the sixth electrode being set at a larger value than
a parasitic capacitance between the fourth electrode and the sixth
electrode.

15. The image display apparatus according to claim 14, whereinthe sixth
electrode is formed such that an area of a part of the sixth electrode
facing the fifth electrode is larger than an area of a part of the sixth
electrode facing the fourth electrode.

16. The image display apparatus according to claim 14, whereinthe
parasitic capacitance between the fifth electrode and the sixth electrode
is set at a value that is twice or more larger than the parasitic
capacitance between the fourth electrode and the sixth electrode.

17. The image display apparatus according to claim 14, whereinthe first
transistor and the second transistor are n-type transistors,a potential
applied to the eighth electrode in a compensation period is set at a
potential that is higher than a maximum value of the potential applied to
the eighth electrode in a writing period,in the compensation period,
charge corresponding to a threshold voltage of the first transistor is
accumulated in the capacitor while the second transistor is set in a
conducting state in which current can flow between the fourth electrode
and the fifth electrode, andin the writing period, charge corresponding
to the emission luminance of the light-emitting device is accumulated in
the capacitor.

18. The image display apparatus according to claim 14, whereinthe first
transistor and the second transistor are p-type transistors,a potential
applied to the eighth electrode in a compensation period is set at a
potential that is lower than a maximum value of the potential applied to
the eighth electrode in a writing period,in the compensation period,
charge corresponding to a threshold voltage of the first transistor is
accumulated in the capacitor while the second transistor is set in a
conducting state in which current can flow between the fourth electrode
and the fifth electrode,in the writing period, charge corresponding to
the emission luminance of the light-emitting device is accumulated in the
capacitor.

19. The image display apparatus according to claim 14, whereinthe first
transistor and the second transistor are n-type transistors,a control
section is provided to control a potential,a first potential is applied
to the second electrode in a compensation period,in the compensation
period, charge corresponding to a threshold voltage of the first
transistor is accumulated in the capacitor while the second transistor is
set in a conducting state in which current can flow between the fourth
electrode and the fifth electrode so as to compensate for the threshold
voltage,the second transistor changes from the conducting state to a
non-conducting state where current cannot flow between the fourth
electrode and the fifth electrode, andat approximately the same time, the
potential applied to the second electrode varies from the first potential
to a second potential that is higher than the first potential.

20. The image display apparatus according to claim 14, whereinthe first
transistor and the second transistor are p-type transistors,a control
section is provided to control a potential,a first potential is applied
to the second electrode in a compensation period,in the compensation
period, charge corresponding to a threshold voltage of the first
transistor is accumulated in the capacitor while the second transistor is
set in a conducting state in which current can flow between the fourth
electrode and the fifth electrode so as to compensate for the threshold
voltage,the second transistor changes from the conducting state to a
non-conducting state where current cannot flow between the fourth
electrode and the fifth electrode, andat approximately the same time, the
potential applied to the second electrode varies from the first potential
to a second potential that is lower than the first potential.

21. An image display apparatus comprising:a light-emitting device of which
emission luminance varies with the amount of current;a first transistor
having first electrode, second electrode and third electrode, wherein the
amount of current between the first electrode and the second electrode is
adjusted by a potential applied to the third electrode;a second
transistor having fourth electrode, fifth electrode and sixth electrode,
whereinthe amount of current between the fourth electrode and the fifth
electrode is adjusted by a potential applied to the sixth electrode; anda
capacitor having seventh electrode and eighth electrode and forming a
capacitance between the seventh electrode and the eighth electrode,the
first electrode being electrically connected to the light-emitting
device, wherein the amount of current in the light-emitting device is
controlled by adjusting the amount of current between the first electrode
and the second electrode,the fourth electrode being electrically
connected to the first electrode, the fifth electrode being electrically
connected to the third electrode,the seventh electrode being electrically
connected to the third electrode.

22. The image display apparatus according to claim 21, whereinthe first
transistor and the second transistor are n-type transistors, anda control
section is provided to control a potential,a first potential is applied
to the second electrode in a compensation period,in the compensation
period, charge corresponding to a threshold voltage of the first
transistor is accumulated in the capacitor while the second transistor is
set in a conducting state in which current can flow between the fourth
electrode and the fifth electrode so as to compensate for the threshold
voltage,the second transistor changes from the conducting state to a
non-conducting state where current cannot flow between the fourth
electrode and the fifth electrode, andat approximately the same time, the
potential applied to the second electrode varies from the first potential
to a second potential that is higher than the first potential.

23. The image display apparatus according to claim 21, whereinthe first
transistor and the second transistor are p-type transistors, anda control
section is provided to control a potential,a first potential is applied
to the second electrode in a compensation period,in the compensation
period, charge corresponding to a threshold voltage of the first
transistor is accumulated in the capacitor while the second transistor is
set in a conducting state in which current can flow between the fourth
electrode and the fifth electrode so as to compensate for the threshold
voltage,the second transistor changes from the conducting state to a
non-conducting state where current cannot flow between the fourth
electrode and the fifth electrode, andat approximately the same time, the
potential applied to the second electrode varies from the first potential
to a second potential that is lower than the first potential.

24. A method for driving an image display apparatus,the image display
apparatus comprising:a light-emitting device of which emission luminance
varies with the amount of current;a first transistor having first
electrode, second electrode and third electrode, wherein the amount of
current between the first electrode and the second electrode is adjusted
by a potential applied to the third electrode;a second transistor having
fourth electrode, fifth electrode and sixth electrode, wherein the amount
of current between the fourth electrode and the fifth electrode is
adjusted by a potential applied to the sixth electrode; anda capacitor
having seventh electrode and eighth electrode and forming a capacitance
between the seventh electrode and the eighth electrode,the first
electrode being electrically connected to the light-emitting device,
wherein the amount of current in the light-emitting device is controlled
by adjusting the amount of current between the first electrode and the
second electrode,the fourth electrode being electrically connected to the
first electrode, the fifth electrode being electrically connected to the
third electrode,the seventh electrode being electrically connected to the
third electrode,the method comprising:a threshold compensation step in
which a first potential is applied to the second electrode, and charge
corresponding to a threshold voltage of the first transistor is
accumulated in the capacitor while the second transistor is set in a
conducting state where current can flow between the fourth electrode and
the fifth electrode so as to compensate for the threshold voltage; anda
step in which the potential applied to the second electrode is varied
from the first potential to a second potential at approximately the same
time as a timing with which the second transistor varies from the
conducting state to a non-conducting state where current cannot flow
between the fourth electrode and the fifth electrode.

25. The image display apparatus driving method according to claim 24,
whereinthe first transistor and the second transistor are n-type
transistors, andthe second potential is higher than the first potential.

26. The image display apparatus driving method according to claim 24,
whereinthe first transistor and the second transistor are p-type
transistors, andthe second potential is lower than the first potential.

[0003]In an organic EL device, for example, a transparent electrode and a
metal electrode are placed opposite to each other, with organic layers,
including a light-emitting layer, being sandwiched between them. In an
organic EL device thus structured, when a voltage or current is applied
across the transparent electrode and the metal electrode, current flows
in the light-emitting layer and the light-emitting layer emits light, and
the light emitted from the light-emitting layer passes through the
transparent electrode to the outside. It is known that, for common
organic EL devices, the current density of the light-emitting layer and
the luminance are nearly proportional to each other, and a conventional
example thereof is disclosed in a patent document (Japanese Patent
Application Laid-Open No. 2006-309258), for example.

[0004]However, the deterioration of the organic EL devices is promoted as
the current density of the organic EL devices is higher, leading to
shorter life of the organic EL devices, and further to shorter life of
the image display apparatus.

DISCLOSURE OF THE INVENTION

[0005]The present invention has been made by considering the problem
above, and an object of the present invention is to provide a technique
that enables longer life of an image display apparatus.

[0006]In order to solve the problem above, an image display apparatus
according to a first aspect of the present invention includes: a
light-emitting device of which emission luminance varies with the amount
of current; and a first transistor having first electrode, second
electrode and third electrode, wherein the amount of current between the
first electrode and the second electrode is adjusted by a potential
applied to the third electrode.

[0007]The image display apparatus further includes: a second transistor
having fourth electrode, fifth electrode and sixth electrode, wherein the
amount of current between the fourth electrode and the fifth electrode is
adjusted by a potential applied to the sixth electrode; and a capacitor
having seventh electrode and eighth electrode and forming a capacitance
between the seventh electrode and the eighth electrode. The first
electrode is electrically connected to the light-emitting device, and the
amount of current in the light-emitting device is controlled by adjusting
the amount of current between the first electrode and the second
electrode. The fourth electrode is electrically connected to the first
electrode, and the fifth electrode is electrically connected to the third
electrode, and the seventh electrode is electrically connected to the
third electrode. A parasitic capacitance between the fifth electrode and
the sixth electrode is set at a larger value than a parasitic capacitance
between the fourth electrode and the sixth electrode.

[0008]A method for driving an image display apparatus according to a
second aspect of the present invention is a method for driving an image
display apparatus that includes: a first transistor having first
electrode, second electrode and third electrode, wherein the amount of
current between the first electrode and the second electrode is adjusted
by a potential applied to the third electrode; a second transistor having
fourth electrode, fifth electrode and sixth electrode, wherein the amount
of current between the fourth electrode and the fifth electrode is
adjusted by a potential applied to the sixth electrode; and a capacitor
having seventh electrode and eighth electrode and forming a capacitance
between the seventh electrode and the eighth electrode. The first
electrode is electrically connected to the light-emitting device, and the
amount of current in the light-emitting device is controlled by adjusting
the amount of current between the first electrode and the second
electrode; the fourth electrode is electrically connected to the first
electrode, the fifth electrode is electrically connected to the third
electrode, and the seventh electrode is electrically connected to the
third electrode. The driving method includes: a threshold compensation
step in which a first potential is applied to the eighth electrode, and
charge corresponding to a threshold voltage of the first transistor is
accumulated in the capacitor while the second transistor is set in a
conducting state where current can flow between the fourth electrode and
the fifth electrode so as to compensate for the threshold voltage; and a
writing step in which a second potential is applied to the eighth
electrode and charge corresponding to the emission luminance of the
light-emitting device is accumulated in the capacitor.

[0009]A method for driving an image display apparatus according to a third
aspect of the present invention is a method for driving an image display
apparatus that includes: a light-emitting device of which emission
luminance varies with the amount of current; a first transistor having
first electrode, second electrode and third electrode, wherein the amount
of current between the first electrode and the second electrode is
adjusted by a potential applied to the third electrode; a second
transistor having fourth electrode, fifth electrode and sixth electrode,
wherein the amount of current between the fourth electrode and the fifth
electrode is adjusted by a potential applied to the sixth electrode; and
a capacitor having seventh electrode and eighth electrode and forming a
capacitance between the seventh electrode and the eighth electrode. The
first electrode is electrically connected to the light-emitting device,
and the amount of current in the light-emitting device is controlled by
adjusting the amount of current between the first electrode and the
second electrode; the fourth electrode is electrically connected to the
first electrode, the fifth electrode is electrically connected to the
third electrode, and the seventh electrode is electrically connected to
the third electrode. The driving method includes: a threshold
compensation step in which a first potential is applied to the second
electrode, and charge corresponding to a threshold voltage of the first
transistor is accumulated in the capacitor while the second transistor is
set in a conducting state where current can flow between the fourth
electrode and the fifth electrode so as to compensate for the threshold
voltage; and a step in which the potential applied to the second
electrode is varied from the first potential to a second potential at
approximately the same time as a timing with which the second transistor
varies from the conducting state to a non-conducting state where current
cannot flow between the fourth electrode and the fifth electrode.

[0010]<Explanation of Terms>

[0011]In this specification, "gate voltage" means the gate potential with
respect to the source, and it is represented also as "Vgs".

[0012]Also, in this specification, "threshold voltage" means the gate
voltage as a boundary at which a transistor changes from the off state
(i.e. a state in which drain current does not flow) to the on state (a
state in which drain current flows), and "threshold voltage" is also
represented simply as "threshold".

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a diagram illustrating a pixel circuit 7 of an image
display apparatus according to a technique compared with the present
invention.

[0014]FIG. 2 is a diagram schematically illustrating parasitic
capacitances generated in the pixel circuit 7 of the technique compared
with the present invention.

[0015]FIG. 3 is a timing chart illustrating driving waveforms for the
image display apparatus of the technique compared with the present
invention.

[0016]FIG. 4 is a circuit diagram illustrating the operation of the pixel
circuit 7 of the technique compared with the present invention.

[0017]FIG. 5 is a circuit diagram illustrating the operation of the pixel
circuit 7 of the technique compared with the present invention.

[0018]FIG. 6 is a circuit diagram illustrating the operation of the pixel
circuit 7 of the technique compared with the present invention.

[0019]FIG. 7 is a circuit diagram illustrating the operation of the pixel
circuit 7 of the technique compared with the present invention.

[0020]FIG. 8 is a circuit diagram illustrating the operation of the pixel
circuit 7 of the technique compared with the present invention.

[0021]FIG. 9 is a diagram illustrating the relation between the voltage
across the gate-source and the current between the drain-source in the
driving transistor of the technique compared with the present invention.

[0022]FIG. 10 is a diagram illustrating variations with time of the
voltage value across the gate-source in the driving transistor that are
exhibited when Vth compensation period is set at 2 ms in the technique
compared with the present invention.

[0023]FIG. 11 is a diagram illustrating variations with time of the
voltage value across the drain-source in the driving transistor that are
exhibited when Vth compensation period is set at 2 ms in the technique
compared with the present invention.

[0024]FIG. 12 is a diagram illustrating variations with time of the
voltage value across the gate-source in the driving transistor that are
exhibited when Vth compensation period is set at 0.2 ms in the technique
compared with the present invention.

[0025]FIG. 13 is a diagram illustrating variations with time of the
voltage value across the drain-source in the driving transistor that are
exhibited when Vth compensation period is set at 0.2 ms in the technique
compared with the present invention.

[0026]FIG. 14 is a diagram illustrating the outline configuration of an
image display apparatus 1A according to a first preferred embodiment of
the present invention.

[0027]FIG. 15 is a block diagram illustrating the configuration of the
display section 200 of the first preferred embodiment of the present
invention.

[0028]FIG. 16 is a diagram illustrating a pixel circuit 7A of the image
display apparatus 1A according to the first preferred embodiment of the
present invention.

[0029]FIG. 17 is a diagram schematically illustrating parasitic
capacitances generated in the pixel circuit 7A of the first preferred
embodiment of the present invention.

[0030]FIG. 18 is a timing chart illustrating driving waveforms for the
pixel circuit 7A of the first preferred embodiment of the present
invention.

[0031]FIG. 19 is a diagram illustrating variations with time of the
gate-source voltage of the driving transistor of the first preferred
embodiment of the present invention.

[0032]FIG. 20 is a diagram illustrating variations with time of the
drain-source voltage of the driving transistor of the first preferred
embodiment of the present invention.

[0033]FIG. 21 is a timing chart illustrating driving waveforms according
to a second preferred embodiment of the present invention.

[0034]FIG. 22 is a timing chart illustrating driving waveforms according
to a third preferred embodiment of the present invention.

[0035]FIG. 23 is a timing chart illustrating driving waveforms for an
image display apparatus according to a modification.

[0036]FIG. 24 is a diagram illustrating a pixel circuit 7P of an image
display apparatus according to a modification.

[0037]FIG. 25 is a timing chart illustrating driving waveforms for an
image display apparatus according to a modification.

[0038]FIG. 26 is a timing chart illustrating driving waveforms for an
image display apparatus according to a modification.

[0039]FIG. 27 is a timing chart illustrating driving waveforms for an
image display apparatus according to a modification.

[0040]FIG. 28 is a timing chart illustrating driving waveforms for an
image display apparatus according to a modification.

BEST MODE FOR CARRYING OUT THE INVENTION

[0041]Now, the preferred embodiments of the present invention will be
described referring to the drawings.

[0042]Before describing the preferred embodiments, an image display
apparatus as a comparison with the image display apparatus of the
preferred embodiments of the invention described later (an image display
apparatus according to a comparative technique) will be described
referring to FIGS. 1 to 13. Now, the image display apparatus has an
organic EL display in which, generally, emission luminance is adjusted
with current value. In this image display apparatus, a large number of
pixels are arranged with an organic EL device provided in each pixel.

[0043]<Configuration of Pixel Circuit>

[0044]FIG. 1 is a diagram illustrating an example configuration of a pixel
circuit (driving circuit) 7 for one pixel in the image display apparatus
of the comparative technique.

[0046]The organic EL device 1. made of organic matter and the like, is a
light-emitting device of which emission luminance varies with the amount
of current flowing in the light-emitting layer. The organic EL device 1
has an anode electrode 1a and a cathode electrode 1b, and the anode
electrode 1a is electrically connected to a VDD line Lvd as a
power-supply line serving as the high-potential side when the organic EL
device 1 emits light. The cathode electrode 1b is electrically connected
through the driving transistor 2 to a VSS line Lvs as a power-supply line
serving as the low-potential side when the organic EL device 1 emits
light.

[0047]The driving transistor 2 is electrically connected in series with
the organic EL device 1, and this is a transistor that controls the
emission luminance of the organic EL, device 1 by adjusting the amount of
current in the organic EL device 1. Here, the driving transistor 2 is
formed of a thin film transistor (TFT) that is a kind of field effect
transistor (FET) adopting MIS (Metal Insulator Semiconductor) structure
of a type (n type) where the carriers are electrons, i.e. an n-MISFETTFT.

[0048]The driving transistor 2 has first to third electrodes 2ds, 2sd and
2g. The first electrode 2ds is electrically connected to the cathode
electrode 1b of the organic EL device 1, and it functions as the drain
electrode (hereinafter referred to simply as "drain") when the organic EL
device 1 emits light, i.e. when forward current flows to the organic EL
device 1. It functions as the source electrode (hereinafter referred to
simply as "source") when reverse current flows to the organic EL device
1. The second electrode 2sd is electrically connected to the VSS line
Lvs, and it functions as the source electrode (source) when forward
current flows to the organic EL device 1. It functions as the drain
electrode (drain) when reverse current flows to the organic EL device 1.
The third electrode 2g is a so-called gate electrode (hereinafter
referred to simply as "gate") and it is electrically connected to one
electrode (seventh electrode 4a) of the capacitor 4.

[0049]In the driving transistor 2, the amount of current flowing between
the first electrode 2ds and the second electrode 2sd (hereinafter also
referred to as "between the first-second electrodes") is adjusted by
adjusting the potential applied to the third electrode 2g, more
specifically the voltage value applied across the first electrode 2ds or
second electrode 2sd and the third electrode 2g (i.e. across the gate and
source). With the potential applied to the third electrode (gate) 2g, the
driving transistor 2 is selectively set in a state where current can flow
(a conducting state) between the first-second electrodes (i.e. between
the drain and source) and a state where current cannot flow (a
non-conducting state).

[0050]The Vth compensation transistor 3 is a transistor that detects the
lower-limit value (a given threshold voltage Vth) of the potential of the
third electrode 2g of the driving transistor 2 with respect to the second
electrode 2sd when the driving transistor 2 goes into the conducting
state, and that adjusts the gate voltage of the driving transistor 2 to
the threshold voltage Vth (hereinafter referred to simply as "threshold
Vth"). Here, like the driving transistor 2, the Vth compensation
transistor 3 is also formed of an n-MISFETTFT.

[0051]The Vth compensation transistor 3 has fourth to sixth electrodes
3ds, 3sd and 3g. The fourth electrode 3ds is conductively connected to
the interconnection that electrically connects the first electrode 2ds of
the driving transistor 2 and the cathode electrode 1b of the organic EL
device 1. That is, the fourth electrode 3ds is electrically connected to
the first electrode 2ds of the driving transistor 2. The fifth electrode
3sd is conductively connected, at a connection point T1, to the
interconnection that electrically connects the third electrode (gate) 2g
of the driving transistor 2 and the capacitor 4. That is, it is
electrically connected to the gate 2g of the driving transistor 2. Also,
the sixth electrode 3g is a so-called gate electrode, which is
electrically connected to a scanning signal line Lss.

[0052]In the Vth compensation transistor 3, the amount of current flowing
(the amount of current) between the fourth electrode 3ds and the fifth
electrode 3sd (hereinafter also referred to as "between the fourth-fifth
electrodes) is adjusted by adjusting the potential applied to the sixth
electrode 3g, more specifically the voltage value applied across the
fourth electrode 3ds or fifth electrode 3sd and the sixth electrode 3g
(i.e. across the gate and source). With the potential applied to the
sixth electrode (gate) 3g, the Vth compensation transistor 3 is
selectively set in a state where current can flow (a conducting state)
between the fourth-fifth electrodes (between the drain and source), and a
state where current cannot flow (a non-conducting state).

[0053]Now, in the organic EL device 1, the emission luminance is
controlled with the current value, so that the emission luminance
sensitively varies with the variation of the gate voltage of the driving
transistor 2 during emission. Particularly, when the driving transistor 2
is made of amorphous silicon, the threshold Vth tends to vary among
driving transistors 2. Accordingly, desired emission luminance and actual
emission luminance differ in the absence of a function of compensating
for the threshold Vth that differs among pixels (Vth compensation
function), leading to unevenness of emission luminance among pixels.

[0054]Accordingly, the Vth compensation transistor 3 is provided to
realize the Vth compensation function of compensating for the variation
of threshold Vth of driving transistors 2 by adjusting the gate voltage
of the driving transistor 2 of each pixel to the threshold Vth before
light is emitted.

[0055]The capacitor 4 includes a seventh electrode 4a electrically
connected to the third electrode 2g of the driving transistor 2. and an
eighth electrode 4b electrically connected to an image signal line Lis.
The capacitance held by the capacitor 4 is represented as a given value
Cs.

[0056]Now, when voltage reverse to that for light emission is applied, the
organic EL device 1 functions as a capacitor, and its capacitance (EL
device capacitance) is represented as a given value Co. Also, the driving
transistor 2 has a parasitic capacitance CgsTd between the second
electrode 2sd and the third electrode 2g (hereinafter also referred to as
"between the second-third electrodes") and a parasitic capacitance CgdTd
between the first electrode gds and the third electrode 2g (hereinafter
also referred to as "between the first-third electrodes"). Also, the Vth
compensation transistor 3 has a parasitic capacitance CgsTth between the
fifth electrode 3sd and the sixth electrode 3g (hereinafter also referred
to as "between the fifth-sixth electrodes") and a parasitic capacitance
CgdTth between the fourth electrode 3ds and the sixth electrode 3g
(hereinafter also referred to as "between the fourth-sixth electrodes").
The parasitic capacitances CgsTd. CgdTd. CgsTth and CgdTth are
capacitances of given values that are determined by the structures
respectively of the driving transistor 2 and the Vth compensation
transistor 3.

[0057]FIG. 2 is a schematic diagram in which the circuit configuration
with the parasitic capacitances CgsTth, CgdTth. CgsTd and CgdTd and the
EL device capacitance Co (drawn in thin line) is added to the circuit
configuration of the pixel circuit 7 shown in FIG. 1 (drawn in thick
line).

[0058]As shown in FIG. 2, in the pixel circuit 7, a capacitor (element
capacitor) 1c having the EL device capacitance Co exists between the two
electrodes of the organic EL device 1, a capacitor 2gs having the
parasitic capacitance CgsTd exists between the second-third electrodes of
the driving transistor 2, and a capacitor 2gd having the parasitic
capacitance CgdTd exists between the first-third electrodes of the
driving transistor 2. Also, a capacitor 3gs having the parasitic
capacitance CgsTth exists between the fifth-sixth electrodes of the Vth
compensation transistor 3, and a capacitor 3gd having the parasitic
capacitance CgdTth exists between the fourth-sixth electrodes of the Vth
compensation transistor 3.

[0059]The description above focuses upon one pixel circuit 7, but a large
number of pixel circuits 7 exist in the entire organic EL display.
Accordingly, there are a large number of scanning signal lines Lss. The
large number of scanning signal lines Lss may hereinafter be referred to
as "Nth scanning signal line (N is a natural number) Lss".

[0060]<Driving Method for Light Emission of Organic EL Device>

[0061]FIG. 3 is a timing chart illustrating signal waveforms (driving
waveforms) for causing the organic EL device 1 to emit light. In FIG. 3,
the horizontal axis indicates time, and the waveforms shown sequentially
from top to bottom are (a) the potential applied to the VDD line Lvd
(potential Vdd), (h) the potential applied to the VSS line Lvs (potential
Vss), (c) the potential of signal applied to a first scanning signal line
Lss (potential Vls1), (d) the potential of signal applied to the second
scanning signal line Lss (potential Vls2), and (e) the potential of
signal applied to the image signal line Lis (potential Vlis).

[0062]FIG. 3 shows driving waveforms for causing the organic EL device 1
to emit light once, and the period for one light emission includes, in
time sequential order, Cs initialization period P1 (time t11 to t12),
preparatory period P2 (time t12 to t13), Vth compensation period P3 (time
t13 to t14), writing period P4 (time t14 to t15), element initialization
period P5 (time t15 to t16), and light emission period P6 (time from
t16). The potential Vlis in the writing period P4 is an arbitrary value
that is determined by the emission luminance of each organic EL device 1,
and therefore, in FIG. 3, the range where the potential can exist is
shown with oblique hatching for the sake of convenience.

[0063]FIGS. 4 to 8 are diagrams illustrating the flow of current in the
pixel circuit 7 that is generated in each period when the image display
apparatus of the comparative technique is driven. In FIGS. 4 to 8, in the
pixel circuit 7, circuits contributing to the flow of current are shown
in thick line, and circuits hardly contributing to the flow of current
are shown in thin line.

[0064]Now, referring to FIGS. 3 and 4 to 8, a method for driving the image
display apparatus of the comparative technique will be described.

[0065]Cs Initialization Period P1:

[0066]FIG. 4 illustrates the flow of current in the pixel circuit 7 during
the Cs initialization period P1 (hereinafter also referred to simply as
"period P1").

[0067]In the period P1, a given positive high potential VDD (e.g. 15 V) is
applied to the VDD line Lvd and the VSS line Lvs, a given positive high
potential VgH (e.g. 15 V) is applied to all scanning signal lines Lss,
and a given reference potential (0 V here) is applied to the image signal
line Lis.

[0068]At this time, for the Vth compensation transistor 3, with the
application of the high potential VgH to the scanning signal line Lss, a
positive potential corresponding to the high potential VgH is applied to
the sixth electrode (gate) 3g, and it becomes conductive. On the other
hand, the driving transistor 2 is off and non-conductive because the VDD
line Lvd and the VSS line Lvs are at approximately equal potentials.

[0069]Thus, in the period P1 as shown by blank arrows in FIG. 4, current
flows from the VDD line Lvd to the capacitor 4 through the fourth and
fifth electrodes 3ds and 3sd of the Vth compensation transistor 3, and a
given amount of charge (e.g. an amount of charge corresponding to 15 V)
is accumulated in the capacitor 4.

[0070]As time passes in the period P1, the amount of charge accumulated in
the capacitor 4 increases, and then a positive potential over a given
value is applied to the third electrode (gate) 2g of the driving
transistor 2, and it may become conductive. However, no current flows
between the first-second electrodes of the driving transistor 2 because
the VDD line Lvd and the VSS line Lvs are both set at the same potential
VDD.

[0071]Preparatory Period P2:

[0072]FIG. 5 illustrates the flow of current in the pixel circuit 7 during
the preparatory period P2 (hereinafter also referred to simply as "period
P2").

[0073]In the period P2, a negative given potential Vp (e.g. -7V) is
applied to the VDD line Lvd, a given reference potential (0 V here) is
applied to the VSS line Lvs, a given low potential VgL (e.g. -10 V) is
applied to all scanning signal lines Lss, and a given high potential VdH
(e.g. 10 V) is applied to the image signal line Lis.

[0074]At this time, for the Vth compensation transistor 3, with the
application of the low potential VgL to the scanning signal line Lss,
almost no positive potential is applied to the sixth electrode (gate) 3g,
and it becomes non-conductive. For the driving transistor 2, with the
application of the high potential VdH to the image signal line Lis, a
positive potential (e.g. 15+10=25 V) corresponding to the high potential
VdH is applied to the third electrode (gate) 2g, and it becomes
conductive.

[0075]Then, since the VSS line Lvs is higher in potential by Vp than the
VDD line Lvd, as shown by blank arrows in FIG. 5, current flows from the
VSS line Lvs to the organic EL device 1 through the second and first
electrodes 2sd and 2ds of the driving transistor 2. As a result, a given
amount of charge corresponding to the potential difference between the
VDD line Lvd and the VSS line Lvs (e.g. charge corresponding to 7 V) is
accumulated in the organic EL device 1, i.e. in the element capacitor 1c.

[0076]Vth Compensation Period P3:

[0077]FIG. 6 illustrates the flow of current in the pixel circuit 7 during
the Vth compensation period P3 (hereinafter also referred to simply as
"period P3").

[0078]In the period P3, a given reference potential (0 V here) is applied
to the VDD line Lvd and the VSS line Lvs, the high potential VgH is
applied to all scanning signal lines Lss, and the high potential Val
(e.g. 10 V) is applied to the image signal line Lis.

[0079]At this time, for the Vth compensation transistor 3, with the
application of the high potential VgH to the scanning signal line Lss, a
positive potential corresponding to the high potential VgH is applied to
the sixth electrode (gate) 3g, and it becomes conductive. Also, in a
first part of the period P3, the driving transistor 2 becomes conductive
because of the charge accumulated in the capacitor 4 and the potential
Val applied to the image signal line Lis.

[0080]Accordingly, in the first part of the period P3, as shown by blank
arrows in FIG. 6, current due to the charge accumulated in the capacitor
4 flows from the capacitor 4 to the fifth and fourth electrodes 3sd and
3ds of the Vth compensation transistor 3, and also flows to the VSS line
Lvs through the first and second electrodes 2ds and 2sd of the driving
transistor 2. Also, current due to the charge accumulated in the element
capacitor 1c flows to the VSS line Lvs through the first and second
electrodes 2ds and 2sd of the driving transistor 2.

[0081]However, as the current due to the charge accumulated in the
capacitor 4 flows from the capacitor 4 to the VSS line Lvs, the charge
accumulated in the capacitor 4 decreases. Then, when the potential Vgs at
the third electrode 2g of the driving transistor 2 with respect to the
second electrode 2sd (hereinafter also referred to as "between the
third-second electrodes") decreases to the threshold Vth, the driving
transistor 2 becomes non-conductive. At this time, charge corresponding
to the threshold Vth is accumulated in the capacitor 4. In this way, in
the period P3, charge corresponding to the threshold Vth is accumulated
in the capacitor 4, and thus variations of the threshold Vth, varying
among pixels, are compensated for.

[0082]Writing Period P4:

[0083]FIG. 7 illustrates the flow of current in the pixel circuit 7 during
the writing period P4 (hereinafter also referred to simply as "period
P4").

[0084]In the period P4, the reference potential 0 V is applied to the VDD
line Lvd and the VSS line Lys, the high potential VgH is applied to the
scanning signal line Lss for a pixel subjected to the processing of
accumulating charge in correspondence with the pixel data signal (data
writing processing), and a potential (VdH-Vdata) is applied to the image
signal line Lis. The potential Vdata is the potential of the pixel data
signal, which is a potential corresponding to the value corresponding to
the tone of the luminance of the pixel forming the image.

[0085]At this time, for the Vth compensation transistor 3, with the
application of the high potential VgH to the scanning signal line Lss, a
positive potential corresponding to the high potential VgH is applied to
the gate, and it becomes conductive. On the other hand, for the driving
transistor 2, because the potential (VdH-Vdata) below the potential VdH
in the period P3 is applied to the image signal line Lis, the gate
voltage goes below the threshold Vth and it becomes non-conductive.

[0086]Thus, in the period P4, as shown by blank arrows in FIG. 7, current
flows from the organic EL device 1 (i.e. the element capacitor 1c) to the
capacitor 4 through the fourth and fifth electrodes 3ds and 3sd of the
Vth compensation transistor 3. As a result, the charge corresponding to
the potential Vdata is added to and accumulated over the charge
corresponding to the threshold Vth already accumulated in the capacitor
4. That is, in the period P4, charge corresponding to the emission
luminance of the organic EL device 1 is accumulated in the capacitor 4.
In other words, in the period P4, in the pixel circuit 7, charge
corresponding to the pixel data signal is accumulated in the capacitor 4.

[0087]The amount of variation of the potential of the seventh electrode 4a
of the capacitor 4 (the gate potential of the driving transistor 2) is a
product of the amount of variation of the potential of the image signal
line Lis and the ratio between the capacitance Cs held in the capacitor 4
and the EL device capacitance Co of the element capacitor 1c (capacitance
ratio). That is, when the potential of the image signal line Lis varies
from VdH to Vdata, the gate potential of the driving transistor 2 varies
by (Vdata-VdH)Cs/(Cs+Co). For example, when VdH=10 V, Vdata=5 V, and
Cs:Co=1:2, the potential of the image signal line Lis varies by ±5 V,
and the gate potential of the driving transistor 2 varies by
(5-10)1/(1+2)=-5/3 V due to the movement of charge from the organic EL
device 1 to the capacitor 4. In this way, the variation of potential on
the image signal line Lis is reflected to the gate potential of the
driving transistor 2 because of the movement of charge accumulated in the
capacitor 4.

[0088]Element Initialization Period P5:

[0089]In the element initialization period P5 (hereinafter also referred
to simply as "period P5"), the given negative potential Vp is applied to
the VDD line Lvd and the VSS line Lvs, the low potential VgL is applied
to all scanning signal lines Lss, and the high potential VdH is applied
to the image signal line Lis. At this time, the Vth compensation
transistor 3 becomes non-conductive, and the driving transistor 2 becomes
conductive. Then, since there is no potential difference between the VDD
line Lvd and the VSS line Lvs and the VSS line Lvs is set at the negative
potential -Vp, the charge accumulated in the organic EL device 1 (i.e.
the element capacitor 1c) flows to the VSS line Lvs, and the charge
accumulated in the organic EL device 1 is discharged.

[0090]Light Emission Period P6:

[0091]FIG. 8 illustrates the flow of current in the pixel circuit 7 during
the light emission period P6 (hereinafter also referred to simply as
"period P6").

[0092]In the period P6, the positive high potential VDD is applied to the
VDD line Lvd. The reference potential 0 V is applied to the VSS line Lvs.
The low potential VgL is applied to the scanning signal line Lss. The
high potential VdH is applied to the image signal line Lis.

[0093]At this time, because of the application of the low potential VgL to
the scanning signal line Lss, the Vth compensation transistor 3 becomes
non-conductive. For the driving transistor 2, due to the application of
the high potential VdH to the image signal line Lis, Vgs becomes higher
than the threshold Vth by the potential corresponding to the amount of
charge accumulated in the capacitor 4 in the period P4 (the amount of
charge corresponding to the potential Vdata), and the driving transistor
2 becomes conductive.

[0094]For example, when Vdata=5 V and Cs:Co=1:2, the charge accumulated in
the capacitor 4 in the period P4 corresponds to a potential lower than
the threshold Vth by 5/3 V ([Vth-5/3] V). Then, in the period P6, a
potential higher than that in the period P4 by Vdata (=5 V) is applied to
the image signal line Lis, and a potential higher than the threshold Vth
by 10/3 V ([Vth+10/3] V=[Vth-(5/3)+5] V) is applied to the third
electrode (gate) 2g.

[0095]Then, the VDD line Lvd is higher in potential than the VSS line Lvs
by the potential VDD, and the driving transistor 2 becomes conductive
where current flows between the first-second electrodes according to the
potential Vdata. Accordingly, as shown by blank arrows in FIG. 8, current
corresponding to the potential Vdata flows to the organic EL device 1. As
a result, the organic EL device 1 emits light with luminance
corresponding to the potential Vdata. That is, in the period P6, light
with luminance corresponding to the pixel data signal is emitted from
each pixel.

[0098]Also, when the current flowing between the first-second electrodes
(between the drain-source) of the driving transistor 2 is represented as
Ids, Expression (2) below holds.

[Expression 2]

Ids=(β/2)×(Vgs-Vth)2=(β/2)×(a×Vdata+d).su-
p.2 (2)

[0099]The emission luminance of the organic EL device 1 is approximately
proportional to the current density flowing in the organic EL device and
desired emission luminance is obtained in each pixel by the control using
the driving waveforms shown in FIG. 3.

[0100]Actual luminance of the screen displayed in the image display
apparatus (i.e. visually recognized luminance) is represented as the
luminance in the period of time-sequential light emission multiplied by
the duty (the ratio of the light emission period P6 in the period of one
frame where the organic EL device 1 emits light once (hereinafter
referred to as "a one-frame period"), i.e. [light emission
period/one-frame period]). For example, when the luminance in the period
P6 is 500 cd/m2 and the duty is 0.4 (i.e. the light emission period
makes up 40%), the actual luminance is 500 cd/m2 multiplied by 0.4
equal to 200 cd/m2.

[0101]Now, as mentioned above, the emission luminance of the organic EL
device 1 is approximately proportional to the current density in the
organic EL device 1, but higher current density flowing in the organic EL
device 1 promotes the deterioration of the organic EL device 1, leading
to shorter life of the organic EL device 1 and further to shorter life of
the image display apparatus.

[0102]Now, one method for lengthening the life of the image display
apparatus is to enhance the duty, intending a reduction of the current
density. Then, increasing the duty requires shortening the periods P1 to
P5 of one-frame period, except the period P6; however, the periods P2, P4
and P5 are already short enough, and a possible approach is to shorten
the Vth compensation period P3.

[0103]However, the inventors of the present invention and others have
found that simply shortening the Vth compensation period P3 causes
various problems. Such problems will be described below.

[0104]FIG. 9 is a diagram illustrating a relation between the potential
difference (voltage value) Vgs between the third-second electrodes (i.e.
between the gate-source) of the driving transistor 2 and the current
value Ids of the current flowing between the first-second electrodes
(i.e. between the drain-source). In FIG. 9, the broken line shows the
relation between the voltage value Vgs and the current value Ids
calculated with Expression (2) above, and the solid line shows the
relation between the voltage value Vgs and the current value Ids obtained
by experiment.

[0105]As is clear from FIG. 9, when the voltage value Vgs is set around
the threshold Vth (about 2.1 V here), the actually measured value of the
current value Ids is larger than the calculated value. That is, in the
driving transistor 2, a current flowing between the drain-source
(hereinafter referred to as "leakage current") is generated even when
voltage value Vgs=threshold Vth.

[0106]FIG. 10 is a diagram illustrating variations with time (actually
measured values) of the potential difference (voltage value) Vgs between
the gate-source of the driving transistor 2 exhibited when the Vth
compensation period P3 is set to 2 milliseconds (ms), and FIG. 11 is a
diagram illustrating variations with time (actually measured values) of
the potential difference (voltage value) Vds between the drain-source of
the driving transistor 2 exhibited when the period P3 is set to 2 ms.
Adjustments were made so that the voltage values Vgs and Vds are both set
at 8 V at the beginning of the period P3.

[0107]The horizontal axes in FIGS. 10 and 11 show elapsed time from the
beginning of the period P3, the vertical axis in FIG. 10 shows the
voltage value Vgs, and the vertical axis in FIG. 11 shows the voltage
value Vds. Also, FIGS. 10 and 11 show, sequentially from top to bottom,
variations with time of the voltage values Vgs and Vds in five kinds of
driving transistors 2 having different thresholds Vth, including a time
variation with threshold Vth=6.2 V (thin line), a time variation with
threshold Vth=5.2 V (thin broken line), a time variation with threshold
Vth=4.2 V (thin chain line), a time variation with threshold Vth=3.2 V
(thick line), and a time variation with threshold Vth=2.2 V (thick broken
line).

[0108]As shown in FIG. 10, the voltage value Vgs reached the threshold Vth
at about 100 μs after the beginning of the period P3, and then
gradually decreased due to the leakage current between the drain-source.
Then, when the process shifts to the period P4 at 2 ms from the beginning
of the period P3, in the gate potential of the driving transistor 2, a
so-called punch-through due to the Vth compensation transistor 3 occurred
(a phenomenon in which the potential varies with parasitic capacitance as
the gate potential of the Vth compensation transistor 3 varies), and the
voltage value Vgs of the driving transistor 2 rapidly dropped by about
0.3 to 0.4 V. After that, the voltage value Vgs of the driving transistor
2 was approximately fixed.

[0109]In this specification, the amount of potential variation of the gate
of the driving transistor 2, which takes place when the Vth compensation
transistor 3 shifts to the non-conductive state due to a variation of the
gate potential of the same, is referred to as "punch-through".

[0110]The voltage value Vgs of the driving transistor 2 is held
approximately constant after the shift to the period P4 because the Vth
compensation transistor 3 goes into the non-conducting state where
current cannot flow between the source-drain and no charge is discharged
from the capacitor 4.

[0111]As to the voltage value Vds due to the charge accumulated in the
organic EL device 1 (i.e. the element capacitor 1c) in the period P2, as
shown in FIG. 11, it rapidly decreased in a first part of the period P3
(till 700 μs from the beginning), and it gradually decreased from a
middle part to last part (700 μs to 2 ms) of the period P3. Then, when
shifting from the period P3 to the period P4, the so-called punch-through
occurred and the voltage value Vds of the driving transistor 2 rapidly
decreased by about 0.5 V. After that, the voltage value Vds of the
driving transistor 2 was approximately fixed.

[0112]The voltage value Vds of the driving transistor 2 is held
approximately fixed after the shift to the period P4 because of the
mechanism shown below. The period P3 is continued for a sufficient time
period after the voltage value Vgs fell below the threshold Vth, and the
voltage value Vgs of the driving transistor 2 is sufficiently lowered due
to the occurrence of leakage current between the drain-source of the
driving transistor 2, as shown in FIG. 9. This results in a condition
where almost no leakage current occurs between the drain-source of the
driving transistor 2, and so almost no charge is discharged from the
element capacitor 1c to the VSS line Lys. Since the amount by which Vgs
falls below Vth does not depend on Vth, just the same offset voltage
occurs in all pixels, and there is no problem in detecting differences in
Vth among pixels.

[0113]FIG. 12 is a diagram illustrating variations with time (actually
measured values) of the potential difference (voltage value) Vgs between
the gate-source of the driving transistor 2 exhibited when the Vth
compensation period P3 is set to 0.2 millisecond (ms), and FIG. 13 is a
diagram illustrating variations with time (actually measured values) of
the potential difference (voltage value) Vds between the drain-source of
the driving transistor 2 exhibited when the period P3 is set to 0.2 ms.
Adjustments were made also here so that the voltage values Vgs and Vds
are both set at 8 V at the beginning of the period P3.

[0114]As in FIGS. 10 and 11, the horizontal axes in FIGS. 12 and 13 show
elapsed time from the beginning of the period P3, the vertical axis in
FIG. 12 shows the voltage value Vgs, and the vertical axis in FIG. 13
shows the voltage value Vds. Also, like FIGS. 10 and 11 FIGS. 12 and 13
show, sequentially from top to bottom, variations with time of the
voltage values Vgs and Vds in five kinds of driving transistors 2 having
different thresholds Vth, including a time variation with threshold
Vth=6.2 V (thin line), a time variation with threshold. Vth=5.2 V (thin
broken line), a time variation with threshold Vth=4.2 V (thin chain
line), a time variation with threshold Vth=3.2 V (thick line), and a time
variation with threshold Vth=2.2 V (thick broken line).

[0115]As shown in FIG. 12, the voltage value Vgs rapidly decreases below
the threshold Vth in the period P3 (elapsed time=0 to 0.2 ms). Then, when
the process shifts to the period P4 at 0.2 ms from the beginning of the
period P3 (elapsed time=0.2 ms), in the gate potential of the driving
transistor 2, a punch-through due to the gate potential variation of the
Vth compensation transistor 3 occurred, and the voltage value Vgs of the
driving transistor 2 rapidly decreased by about 0.3 to 0.4 V. After that,
the voltage value Vgs of the driving transistor 2 was approximately
fixed.

[0116]The voltage value Vgs of the driving transistor 2 is thus held
approximately constant after the shift to the period P4 because the Vth
compensation transistor 3 goes into the non-conducting state where
current cannot flow between the source-drain and no charge is discharged
from the capacitor 4.

[0117]As shown in FIG. 13, the voltage value Vds rapidly decreases during
a first part of the period P3 (elapsed time=0 to 0.2 ms), and the process
shifts from the period P3 to the period P4 in the course of the rapid
decrease. Then, at the shift from the period P3 to the period P4 (elapsed
time=0.2 ms), a so-called punch-through occurred and the voltage value
Vds of the driving transistor 2 rapidly decreased by about 0.5 V. After
that, the voltage value Vds of the driving transistor 2 showed a tendency
to gradually decrease as time passes.

[0118]Thus, after the shift to the period P4, the voltage value Vds of the
driving transistor 2 gradually decreases as time passes because of the
mechanism shown below. The period P3 is continued for just a short time
after the voltage value Vgs fell below the threshold Vth, and the voltage
value Vgs of the driving transistor 2 is not lowered by a sufficient
amount by the leakage current between the drain-source of the driving
transistor 2, and leakage current continuously occurs between the
drain-source of the driving transistor 2, as shown in FIG. 9.
Accordingly, charge is gradually discharged from the element capacitor 1c
to the VSS line Lvs.

[0119]Then, the time from when the process shifts to the period. P4 to
when data writing processing is performed differs depending on the
position of the pixel in the image display apparatus and the method of
driving the image display apparatus, and the amount of discharge of
charge from the element capacitor 1c reaches 0.1 V or more in 300 μs
from the shift to the period P4.

[0120]Thus, when the Vth compensation period P3 is simply shortened, the
amount of charge discharged from the element capacitor 1c differs between
a pixel that is subjected to data writing processing immediately after
the shift to the writing period P4 and a pixel that is subjected to data
writing processing after a considerable time has passed after the shift
to the period P4. Accordingly, the amounts of charge accumulated in the
capacitors 4 in data writing processing vary among elements, and the gate
voltages of the driving transistors 2 in the light emission period P6 are
shifted from desired values, and desired luminance is not obtained in the
screen of the image display apparatus, resulting in unevenness of
luminance.

[0121]Also, in the writing period P4, among a plurality of pixels
connected in common to one image signal line Lis, the potential applied
to the image signal line Lis in the data writing processing to one pixel
affects other pixels not yet subjected to data writing processing.

[0122]More specifically, for example, the potential applied to the image
signal line Lis is relatively low when charge corresponding to high
luminance is accumulated in the capacitor 4 in one pixel, and the
potential applied to the image signal line Lis is relatively high when
charge corresponding to low luminance is accumulated in the capacitor 4.
Thus, when high potential is applied to the image signal line Lis for one
pixel, the high potential is applied to the image signal line Lis also
for another pixel not yet subjected to data writing processing, and the
gate voltage of the driving transistor 2 rises and leakage current is
more likely to occur between the drain-source of the driving transistor
2.

[0123]As a result, desired luminance cannot be obtained when a certain or
larger number of pixels emit light with low luminance in a group of
pixels connected in common to one image signal line Lis. That is,
belt-like unevenness (so-called cross-talk) occurs in the screen of the
image display apparatus depending on the ratio of low-luminance
light-emitting pixels among a plurality of pixels connected in common to
one image signal line Lis.

[0124]Accordingly, the inventors of the present invention and others have
devised an image display apparatus and a method for driving it where
luminance unevenness and cross-talk are less likely to occur in the
screen even when the Vth compensation period P3 is shortened. The
apparatus and method will be described below.

First Preferred Embodiment

[0125]<Outline of Configuration of Image Display Apparatus>

[0126]FIG. 14 is a diagram illustrating the outline of the configuration
of an image display apparatus according a first preferred embodiment of
the present invention.

[0127]A mobile phone 1A is a portable electronic device having a display
control section 100 and a display section 200, which functions as an
image display apparatus that displays various kinds of images, such as
moving pictures, in the display section 200. The mobile phone 1A is
hereinafter referred to also as "an image display apparatus 1A".

[0128]The display control section 100 is a part that controls the image
display in the display section 200 on the basis of image signal.

[0129]The display section 200 is composed of, e.g. an organic EL display
(organic electroluminescence display) having approximately rectangular
contours, and driver means to which various signals supplied from the
display control section 100 are inputted. The organic EL display is a
self-emitting type image display device having self-emitting type
light-emitting elements in which current is applied to organic matter to
cause the material itself to emit light.

[0130]The organic EL display has image signal lines for supplying pixels
with data signal (pixel data signal) corresponding to emission luminance,
and scanning signal lines arranged approximately perpendicular to the
image signal lines, for supplying pixels with scanning signal. The
scanning signal is a signal for controlling the timing with which the
pixel signal is supplied to the pixels through the image signal lines.

[0131]The driver means has an X driver (image signal line driving circuit)
electrically connected to the image signal lines, for controlling the
timing with which the pixel signal is supplied to the image signal lines,
and a Y driver (scanning signal line driving circuit) electrically
connected to the scanning signal lines, for controlling the timing with
which the scanning signal is supplied to the scanning signal lines. For
example, in the mobile phone 1A, the X driver is placed along a shorter
side of the organic EL display, and the Y driver is placed along a longer
side of the organic EL display.

[0132]<Outline of Configuration of Display Section>

[0133]FIG. 15 is a block diagram illustrating the outline of the
configuration of the display section 200. FIG. 15 shows two perpendicular
axes X and Y in order to clarify the orientation.

[0135]The organic EL display AA has a large number of pixel circuits 7A
arranged in a matrix (i.e. in a lattice-like form) along the vertical
direction (Y direction) and the horizontal direction (X direction). Image
signal lines Lis are provided for the respective columns of the pixel
circuits 7A parallel to the Y direction, and each image signal line Lis
is electrically connected in common to a plurality of pixel circuits 7A.
Also, scanning signal lines Lss are provided for the respective rows of
the pixel circuits 7A parallel to the X direction, and each scanning
signal line Lss is electrically connected in common to a plurality of
pixel circuits 7A.

[0136]The timing generating circuit TC sends to the image signal line
driving circuit Xd a signal for controlling the timing with which the
pixel signal is supplied to each image signal line Lis from the image
signal line driving circuit Xd, in synchronization with image data (e.g.
RGB pixel signal) D sent from the display control section 100, and it
also sends to the scanning signal line driving circuit Yd a signal for
controlling the timing with which the scanning signal is supplied to each
scanning signal line Lss from the scanning signal line driving circuit
Yd.

[0137]The image signal line driving circuit. Xd is responsive to the
signal from the timing generating circuit TC to supply the pixel signal
to the image signal lines Lis. The scanning signal line driving circuit
Yd is responsive to the signal from the timing generating circuit TC to
supply the scanning signal to the scanning signal lines Lss. The timing
generating circuit TC thus provides control so that the pixel signal is
properly supplied to each pixel circuit 7A through the image signal lines
Lis.

[0138]The power-supply controller EC is a part that controls the supply of
power to each pixel circuit 7A (specifically, power required for the
emission of light etc.), and it may be realized by hardware, i.e. circuit
configuration, or by performing software with a CPU.

[0139]<Configuration of Pixel Circuit>

[0140]FIG. 16 is a diagram illustrating the configuration of a driving
circuit (pixel circuit) 7A for one pixel in the image display apparatus
1A.

[0141]In the pixel circuit 7A, the Vth compensation transistor 3 of the
pixel circuit 7 of the comparative technique is replaced by a Vth
compensation transistor 3A that has characteristic functions and
structure of the present invention.

[0142]Now, the pixel circuit 7A of the first preferred embodiment will be
described, where parts of the pixel circuit 7A that are equivalent to
those of the pixel circuit 7 are shown with the same reference characters
and not described here again, and differences will be described mainly.

[0143]Like the Vth compensation transistor 3 of the comparative technique,
the Vth compensation transistor 3A detects the lower-limit value
(threshold Vth) of the potential difference (i.e. gate voltage) between
the third-second electrodes (i.e. between the gate-source) of the driving
transistor 2 that allows current to flow between the first-second
electrodes (i.e. between the drain-source) of the driving transistor 2,
and it also adjusts the gate voltage of the driving transistor 2 to the
threshold Vth. Like the Vth compensation transistor 3 of the comparative
technique, the Vth compensation transistor 3A is formed of a so-called
n-MISFETTFT.

[0144]Also, the Vth compensation transistor 3A is electrically connected
to other parts in the same way as the Vth compensation transistor 3 of
the comparative technique. Specifically, the fourth electrode 3ds of the
Vth compensation transistor 3A is conductively connected to the
interconnection that electrically connects the first electrode 2ds of the
driving transistor 2 and the cathode electrode 1b of the organic EL
device 1, whereby it is electrically connected to the first electrode 2ds
of the driving transistor 2.

[0145]Also, the fifth electrode 3sd of the Vth compensation transistor 3A
is conductively connected, at a connection point T1, to the
interconnection that electrically connects the third electrode (gate) 2g
of the driving transistor 2 and the seventh electrode 4a of the capacitor
4, whereby it is electrically connected to the third electrode (gate) 2g
of the driving transistor 2. Also, the sixth electrode (gate) 3g of the
Vth compensation transistor 3A is electrically connected to the scanning
signal line Lss.

[0146]In the Vth compensation transistor 3A, a parasitic capacitance
CgsTthA forms between the sixth-fifth electrodes, and a parasitic
capacitance CgdTthA forms between the sixth-fourth electrodes.

[0147]Like FIG. 2, FIG. 17 is circuit diagram in which the circuit
configuration (shown in thin line) of parasitic capacitances CgsTthA,
CgdTthA, CgsTd and CgdTd and EL device capacitance Co is added to the
circuit configuration of the pixel circuit 7A shown in FIG. 16 (shown in
thick line).

[0148]As shown in FIG. 17, in the pixel circuit 7A, a capacitor (element
capacitor) 1c having the EL device capacitance Co exists between the two
electrodes of the organic EL device 1. A capacitor 2gs having the
parasitic capacitance CgsTd exists between the second-third electrodes of
the driving transistor 2, and a capacitor 2gd having the parasitic
capacitance CgdTd exists between the first-third electrodes of the
driving transistor 2. Also, a capacitor 3Ags having the parasitic
capacitance CgsTthA exists between the fifth-sixth electrodes of the Vth
compensation transistor 3A, and a capacitor 3Agd having the parasitic
capacitance CgdTthA exists between the fourth-sixth electrodes of the Vth
compensation transistor 3A.

[0149]In the pixel circuit 7A, unlike in the comparative technique, the
relation shown by Expression (3) below is satisfied about the parasitic
capacitances CgsTthA and CgdTthA of the Vth compensation transistor 3A,
so that the parasitic capacitance CgsTthA is increased.

[Expression 3]

[CgsTthA]>[CgdTthA] (3)

[0150]As to the method for adjustments to satisfy the relation of
Expression (3), for example, in the element structure of the Vth
compensation transistor 3A, the relation of Expression (3) holds when the
area where the fifth electrode 3sd and the sixth electrode 3g face each
other is larger than the area where the fourth electrode 3ds and the
sixth electrode 3g face each other.

[0151]For example, when the area where the fifth electrode 3sd and the
sixth electrode 3g face each other is twice or more larger than the area
where the fourth electrode 3ds and the sixth electrode 3g face each
other, the parasitic capacitance CgsTthA can be set at a sufficiently
large value that is twice or more larger than the parasitic capacitance
CgdTthA.

[0152]Now, examples will be described where the parasitic capacitances
CgsTth and CgdTth of the comparative technique are both set at 3.6
femtofarads (fF), and the parasitic capacitance CgdTthA of this preferred
embodiment is set at 3.6 fF, and the parasitic capacitance CgsTthA is set
at 18 fF, which is five times the parasitic capacitance CgsTth.

[0153]<Driving Method>

[0154]FIG. 18 is a timing chart illustrating signal waveforms (driving
waveforms) for driving the image display apparatus 1A. In FIG. 18, as in
FIG. 3, the horizontal axis shows time, and the waveforms shown
sequentially from top to bottom are (a) the potential applied to the VDD
line Lvd (potential Vdd), (b) the potential applied to the VSS line Lvs
(potential Vss), (c) the potential of signal applied to a first scanning
signal line Lss (potential Vls1), (d) the potential of signal applied to
a second scanning signal line Lss (potential Vls2), and (e) the potential
of signal applied to the image signal line Lis (potential Vlis).

[0155]Like FIG. 3, FIG. 18 shows driving waveforms for causing the organic
EL device 1 to emit light once, and the period of one light emission
includes, in time sequential order, Cs initialization period P1 (time t1
to t2), preparatory period P2 (time t2 to t3), Vth compensation period P3
(time t3 to t4), writing period P4 (time t4 to t5), element
initialization period P5 (time t5 to t6), and light emission period P6
(time from t6). The potential Vlis in the writing period P4 is an
arbitrary value that is determined by the emission luminance of each
organic EL device 1, and therefore, in FIG. 18, as in FIG. 3, the range
where the potential can exist is shown by oblique hatching for the sake
of convenience.

[0156]When the image display apparatus 1A is driven (specifically, in the
periods P1 to P6), the flow of current in the pixel circuit 7A is similar
to that in the pixel circuit 7 of the comparative technique (i.e. the
flow of current shown in FIGS. 4 to 8), which will therefore not be
described again here. The application of voltage across the VDD line Lvd
and the VSS line Lvs, i.e. the supply of power (feeding) to the pixel
circuit 7A, is controlled by the power-supply controller EC.

[0157]Also, the potentials applied to the individual parts during the
periods P1 to P6 shown in FIG. 18 are the same as those shown in FIG. 3,
which will therefore not be described again here.

[0158]It should be noted that, as to the lengths of the periods P1 to P6
shown in FIG. 18, only the Vth compensation period P3 (the period of time
t3 to t4 shaded with dots in FIG. 18) is shorter than the period P3 shown
in FIG. 3.

[0159]Specifically, the period P1 (time t1 to t2) shown in FIG. 18 has the
same length as the period P1 (time t11 to t12) shown in FIG. 3, the
period P2 (time t2 to t3) shown in FIG. 18 has the same length as the
period P2 (time t12 to t13) shown in FIG. 3, the period P4 (time t4 to
t5) shown in FIG. 18 has the same length as the period P4 (time t14 to
t15) shown in FIG. 3, and the period P5 (time t5 to t6) shown in FIG. 18
has the same length as the period P5 (time t15 to t16) shown in FIG. 3,
while the Vth compensation period P3 (time t3 to t4) shown in FIG. 18 is
shorter than the period P3 (time t13 to t14) shown in FIG. 3. For
example, the period P3 shown in FIG. 3 can be 2 ms, and the period P3
shown in FIG. 18 can be 0.2 ms.

[0160]<Shortening of Vth Compensation Period and its Effects>

[0161]FIG. 19 is a diagram illustrating variations with time (actually
measured values) of the potential difference (voltage value) Vgs between
the third-second electrodes (i.e. between the gate-source) of the driving
transistor 2 exhibited when the Vth compensation period P3 is set to 0.2
ms, and FIG. 20 is a diagram illustrating variations with time (actually
measured values) of the potential difference (voltage value) Vds between
the first-second electrodes (i.e. between the drain-source) of the
driving transistor 2 exhibited when the period P3 is set to 0.2 ms.
Adjustments were made so that the voltage values Vgs and Vds are both set
at 8 V at the beginning of the period P3.

[0162]As in FIGS. 10 and 11, the horizontal axes in FIGS. 19 and 20 show
elapsed time from the beginning of the period P3, the vertical axis in
FIG. 19 shows the voltage value Vgs, and the vertical axis in FIG. 20
shows the voltage value Vds.

[0163]Also, like FIGS. 10 and 11, FIGS. 19 and 20 show, sequentially from
top to bottom, variations with time of the voltage values Vgs and Vds in
five kinds of driving transistors 2 having different thresholds Vth,
including a time variation with threshold Vth=6.2 V (thin line), a time
variation with threshold Vth=5.2 V (thin broken line), a time variation
with threshold Vth=4.2 V (thin chain line), a time variation with
threshold Vth=3.2 V (thick line), and a time variation with threshold
Vth=2.2 V (thick broken line).

[0164]As shown in FIG. 19, the voltage value Vgs rapidly decreases below
the threshold Vth in the period P3 (elapsed time-0 to 0.2 ms). Then, when
the process shifts to the period P4 (elapsed time=0.2 ms), in the gate
potential of the driving transistor 2, a punch-through due to the gate
potential variation of the Vth compensation transistor 3A occurred, and
the voltage value Vgs of the driving transistor 2 rapidly decreased by 1V
or more. After that, the voltage value Vgs of the driving transistor 2
was approximately fixed.

[0165]The voltage value Vgs of the driving transistor 2 is thus held
approximately constant after the shift to the period P4 because the Vth
compensation transistor 3A goes into the no-conducting state in which
current cannot flow between the fourth-fifth electrodes (i.e. between the
drain-source) and no charge is discharged from the capacitor 4.

[0166]Next, as shown in FIG. 20, the voltage value Vds rapidly decreases
in the period P3 (elapsed time=0 to 0.2 ms), and the process shifts from
the period P3 to the period P4 in the course of the rapid decrease. Then,
at the shift from the period P3 to the period P4 (elapsed time=0.2 ms), a
so-called punch-through occurred and the voltage value Vds of the driving
transistor 2 rapidly decreased by about 0.5 V. After that, the voltage
value Vds of the driving transistor 2 was approximately constant.

[0167]The phenomenon in which the voltage value Vds of the driving
transistor 2 is thus held approximately constant after the shift to the
period P4 occurs because of the mechanism shown below. As shown in FIG.
19, the amount by which the voltage value Vgs of the driving transistor 2
rapidly decreases (for example, 1 V or more) due to the punch-through
when the process shifts from the period P3 to the period. P4 is twice or
more larger than the amount by which the voltage value Vgs of the driving
transistor 2 rapidly decreases (for example, about 0.3 to 0.4 V) due to
the punch-through in the comparative technique shown in FIGS. 10 and 12,
whereby the voltage value Vgs of the driving transistor 2 is sufficiently
lowered. As a result, the driving transistor 2 goes into a state where
almost no leakage current occurs between the source-drain, and almost no
charge is discharged from the element capacitor 1c to the VSS line Lys.

[0168]Now, the reason will be described for which the amount of rapid
decrease of the voltage value Vgs of the driving transistor 2 due to the
punch-through is increased.

[0169]The voltage of punch-through of the gate voltage (voltage value Vgs)
of the driving transistor 2 due to the Vth compensation transistor 3A
(punch-through voltage, i.e. the amount of potential variation with
parasitic capacitance when the gate voltage varies) MV is given by
Expression (4) below with the high potential VgH and low potential VgL of
the gate potential of the Vth compensation transistor 3A.

[Expression 4]

MV=CgsTthAx(VgL-VgH)/(Cs+CgsTthA+CgdTd+CgsTd) (4)

[0170]As described above, the relation given by Expression (3) is
satisfied about the parasitic capacitances CgsTthA and CgathA of the Vth
compensation transistor 3 of this preferred embodiment, whereby the
parasitic capacitance CgsTthA is increased. Then, as shown by Expression
(4) when the absolute value of the punch-through voltage increases as the
parasitic capacitance CgsTthA is increased, the gate voltage (voltage
Vgs) of the driving transistor 2 rapidly decreases by a larger amount
when the process moves from the period P3 to the period P4.

[0171]When the amount of rapid decrease of the voltage value Vgs of the
driving transistor 2 is thus increased, the driving transistor 2 goes
into the non-conducting state where current cannot sufficiently flow
between the source-drain. Accordingly, even when the period P3 is
shortened, the amount of charge discharged from the element capacitor 1c
hardly differs between a pixel that is subjected to data writing
processing immediately after the shift to the period P4 and a pixel that
is subjected to data writing processing after a considerable time has
passed after the shift to the period P4. This makes it possible to
shorten the Vth compensation period P3, while suppressing luminance
unevenness and cross-talk on the screen.

[0172]For example, the period P3 can be considerably shortened by 1.8 ms
from 2 ms to 0.2 ms, and this time period (1.8 ms) can be utilized to
prolong the period P6, whereby, when the duty of the comparative
technique is 30%, the duty can be considerably increased to 40.8%. This
increase in duty offers enhanced visible emission luminance, making it
possible to reduce the current density required to realize the same
emission luminance.

[0173]As described so far, in the image display apparatus 1A of the first
preferred embodiment, the parasitic capacitance CgsTthA between the
fifth-sixth electrodes of the Vth compensation transistor 3A is set to be
a larger value than the parasitic capacitance CgdTthA between the
fourth-sixth electrodes. This structure increases the amount of variation
of the gate potential of the driving transistor 2 that occurs when the
Vth compensation transistor 3A changes from the conducting state to the
non-conducting state, whereby the driving transistor 2 goes into the
non-conducting state even when the Vth compensation period P3 is
shortened. As a result, even when the Vth compensation period P3 is
shortened, almost no differences occur in the amount of reduction of
charge accumulated in the organic EL device 1 before charge corresponding
to the image data signal is accumulated in individual pixels during the
writing period P4. This makes it possible to lengthen the life of the
image display apparatus 1A while suppressing luminance unevenness and
cross-talk on the screen.

[0174]Also, when the parasitic capacitance CgsTthA is set sufficiently
larger, twice or more, than the parasitic capacitance CgdTthA, the gate
potential of the driving transistor 2 varies by a considerably increased
amount when the Vth compensation transistor 3A changes from the
conducting state to the non-conducting state. Accordingly, even when the
Vth compensation period P3 is further shortened, the driving transistor 2
can easily go into the non-conducting state when the process moves to the
writing period P4. This makes it possible to further prolong the life of
the image display apparatus 1A while suppressing luminance unevenness and
cross-talk on the screen.

Second Preferred Embodiment

[0175]In the image display apparatus 1A of the first preferred embodiment,
the parasitic capacitance CgsTthA of the Vth compensation transistor 3A
is set at a larger value than the parasitic capacitance CgdTthA so that
the gate potential of the driving transistor 2 is lowered by an increased
amount when the Vth compensation transistor 3A changes from the
conducting state to the non-conducting state, whereby, even when the
period P3 is shortened, the driving transistor 2 can easily go into the
non-conducting state when the process shifts to the period P4. On the
other hand, in an image display apparatus 1B of the second preferred
embodiment, the potential of the signal applied to the image signal line
Lis is appropriately adjusted so that the driving transistor 2 goes into
the non-conducting state at the shift to the period P4, even when the
period P3 is shortened.

[0176]Now, the image display apparatus 1B of the second preferred
embodiment will be described.

[0177]In the description below, parts, periods and potentials similar to
those of the first preferred embodiment are shown with the same reference
characters and not described again here, and differences will be
described mainly.

[0178]FIG. 21 is a timing chart illustrating signal waveforms (driving
waveforms) for driving the image display apparatus 1B. In FIG. 21, as in
FIGS. 3 and 18, the horizontal axis shows time, and the waveforms shown
sequentially from top to bottom are (a) the potential applied to the VDD
line Lvd (potential Vdd), (b) the potential applied to the VSS line Lvs
(potential Vss), (c) the potential of signal applied to the first
scanning signal line Lss (potential Vls1), (d) the potential of signal
applied to the second scanning signal line Lss (potential Vls2), and (e)
the potential of signal applied to the image signal line Lis (potential
Vlis).

[0179]Like FIGS. 3 and 18, FIG. 21 shows driving waveforms for causing the
organic EL device 1 to emit light once, and the period of one light
emission includes, in time sequential order, Cs initialization period P1
(time t1 to t2), preparatory period P2 (time t2 to t3), Vth compensation
period P3 (time t3 to t4), writing period P4 (time t4 to t5), element
initialization period P5 (time t5 to t6), and light emission period P6
(time from t6). The potential Vlis in the writing period P4 is an
arbitrary value that is determined by the emission luminance of each
organic EL device 1, and therefore, in FIG. 21, as in FIGS. 3 and 18, the
range where the potential can exist is obliquely hatched for the sake of
convenience.

[0180]In the driving waveforms shown in. FIG. 21, the four potentials Vdd,
Vss, Vls1, and Vls2 show the same potential waveforms as those shown in
FIG. 18.

[0181]On the other hand, as to the potential (potential Vlis) applied to
the image signal line Lis, the waveform differs from that shown in FIG.
18 in that the potential in time t2 to t4, i.e. in the periods P2 and P3,
is set higher by a certain value a to VdH+α, and the potential
waveform is set in the same way in other respects.

[0182]When the potential Vlis in the periods P2 and P3 is thus set higher
than the given high potential VdH by the given value α, the eighth
electrode 4h of the capacitor 4 is also set to the potential VdH+α,
whereby, in the period P3, the charge accumulated in the capacitor 4 is
discharged to the VSS line Lvs faster and by a larger amount.
Accordingly, even when the period P3 is shortened, the gate voltage Vgs
of the driving transistor 2 is sufficiently lowered, and therefore, in
the period P4, the driving transistor 2 goes into a state where almost no
leakage current occurs between the first-second electrodes. As a result,
in the period P4, charge is less likely to be discharged from the element
capacitor 1c to the VSS line Lvs in pixels that have not yet been
subjected to data writing processing.

[0183]Seen from another aspect, the potential Vlis in the period P3 is set
higher than the maximum value of the potential Vlis in the period P4.
When the potential is set in this way, in the period P4, when data
writing processing is applied to one pixel among a plurality of pixels
connected in common to the same image signal line Lis, leakage current is
less likely to occur in driving transistors 2 in the other pixels.

[0184]By the way, in the driving waveforms shown in FIG. 21, the potential
Vlis is lowered to 0 V at approximately the same time (time t4) as the
Vth compensation transistor 3B goes into the non-conducting state when
the process moves from the period P3 to the period P4. It is preferable
to consider the following point about the relation between the timing
with which the Vth compensation transistor 3B is placed into the
non-conducting state and the timing with which the potential Vlis (i.e.
the potential applied to the eighth electrode 4b) is lowered.

[0185]For example, it is preferable to lower the potential Vlis after the
Vth compensation transistor 3B has been placed in the non-conducting
state. This is because, if some period exists before the Vth compensation
transistor 3B is placed in the non-conducting sate after the potential
Vlis is lowered, charge is accumulated in the capacitor 4 in this period
and it hinders the lowering of the gate voltage Vgs of the driving
transistor 2. However, from the aspect of shortening the period P3, it is
preferable to set as short as possible the period from when the Vth
compensation transistor 3B is placed in the non-conducting state to when
the potential Vlis is lowered. That is, it is most preferable to set the
same the timing with which the Vth compensation transistor 3B is placed
in the non-conducting state and the timing with which the potential Vlis
is lowered.

[0186]While the potential Vlis is set higher by a than VdH in the periods
P2 and P3, the amount of increase "α" of potential can be set as
follows, for example.

[0187]For example, when the threshold voltage Vth=2.2 V, and when, as
shown in FIG. 10, the period P3 is set at 2 ms and the gate voltage Vgs
of the driving transistor 2 is lowered to about 0.9 V in the period P3,
then, as shown in FIG. 11, the driving transistor 2 goes into the
non-conducting state in the period P4. On the other hand, when, as shown
in FIG. 12, the period P3 is shortened to 0.2 ms and the gate voltage Vgs
of the driving transistor 2 is lowered only to about 1.7 V in the period
P2, then, as shown in FIG. 13, leakage current occurs in the driving
transistor 2 in the period P4. Considering this, the period P3 can be
shortened to 0.2 ms when the amount of charge accumulated in the
capacitor 4 at the end of the period P3 is lowered by about 0.8
(=1.7-0.9) V. More specifically, the amount of increase a of the
potential can be set on the basis of the ratio (capacitance ratio) of the
capacitance of the capacitor 4 in the capacitance of the capacitor 4 and
other capacitors.

[0188]In this way, in the image display apparatus 1B of the second
preferred embodiment, the potential Vlis in the period P3 (potential
VdH+α here) is set higher than the maximum value of the potential
Vlis in the period P4 (potential VdH here), With this configuration, even
when the period P3 is shortened, the driving transistor 2 goes into the
non-conducting state where leakage current hardly occurs when the Vth
compensation transistor 3A changes from the conducting state to the
non-conducting state. As a result, even when the period P3 is shortened,
almost no differences occur in the amount of decrease of the charge
accumulated in the organic EL, device 1 before charge corresponding to
the pixel data signal is accumulated in individual pixels during the
period P4. This makes it possible to lengthen the life of the image
display apparatus while suppressing luminance unevenness and cross-talk
on the screen.

[0189]Also, it can be said that the image display apparatus 1B of the
second preferred embodiment is more preferable to the image display
apparatus 1A of the first preferred embodiment in the following aspects.

[0190]The Vth compensation transistor 3B is not larger-sized due to
increased overlap for enlarging the parasitic capacitance VgsTth. That
is, as compared with the image display apparatus 1A of the first
preferred embodiment, the image display apparatus 1B of the second
preferred embodiment can adopt a simpler structure for the pixel circuit
713, though it requires altering the circuit for adjusting the potential
Vlis. This is more preferable because this does not lower the degree of
freedom of design, e.g. this does not reduce the areas for the formation
of the driving transistor 2 and the capacitor 4 that are important to
adjust the emission luminance of the organic EL device 1.

[0191]Also, precisely adjusting the potential Vlis is easier than
precisely adjusting the overlap in the Vth compensation transistor 3A.
Furthermore, this is preferable also in that the potential Vlis can be
adjusted after the pixel circuit 713 has been formed.

Third Preferred Embodiment

[0192]In the image display apparatus 1B of the second preferred
embodiment, the potential Vlis (i.e. the potential of the eighth
electrode 4b of the capacitor 4) is appropriately adjusted so that, even
when the period P3 is shortened, the driving transistor 2 goes into the
non-conducting state when the process shifts to the period P4. On the
other hand, in an image display apparatus 1C of a third preferred
embodiment, the potential applied to the VSS line Lvs (i.e. the potential
applied to the second electrode 2sd of the driving transistor 2) is
appropriately adjusted so that, even when the period P3 is shortened, the
driving transistor 2 goes into the non-conducting state when the process
shifts to the period P4.

[0193]Now, the image display apparatus 1C of the third preferred
embodiment will be described.

[0194]In the description below, parts, periods and potentials similar to
those in the first and second preferred embodiments are shown with the
same reference characters and not described again here, and differences
will be described mainly.

[0195]FIG. 22 is a timing chart illustrating signal waveforms (driving
waveforms) for driving the image display apparatus 1C. In FIG. 22, as in
FIGS. 3, 18 and 21, the horizontal axis shows time, and the waveforms
shown sequentially from top to bottom are (a) the potential applied to
the VDD line Lvd (potential Vdd), (b) the potential applied to the VSS
line Lvs (potential Vss), (c) the potential applied to the first scanning
signal line Lss (potential Vls1), (d) the potential applied to the second
scanning signal line Lss (potential Vls2), and (e) the potential applied
to the image signal line Lis (potential Vlis).

[0196]Like FIGS. 3, 18 and 21, FIG. 22 shows driving waveforms for causing
the organic EL device 1 to emit light once, and the period of one light
emission includes, in time sequential order, Cs initialization period P1
(time t1 to t2), preparatory period P2 (time t2 to t3), Vth compensation
period P3 (time t3 to t4), writing period P4 (time t4 to t5), element
initialization period P5 (time t5 to t6), and light emission period P6
(time from t16). The potential Vlis in the period P4 is an arbitrary
value that is determined by the emission luminance of each organic EL
device 1, and therefore, in FIG. 22, as in FIGS. 3, 18 and 21, the range
where the potential Vlis can exist is shown with oblique hatching for the
sake of convenience.

[0197]In the driving waveforms shown in FIG. 22, the four potentials Vdd,
Vls1, Vls2 and Vlis are the same potential waveforms as those shown in
FIG. 18. On the other hand, as to the potential (potential Vss) applied
to the VSS line Lvs, as compared with that shown in FIG. 18, the
potential in time t2 to t4, i.e. in the periods P2 and P3, is set lower
by a certain value β to -β, and the potential waveform is the
same in other respects.

[0198]In this way, when the potential Vss in the periods P2 and P3 is set
lower by β than 0 V, in the period P3, the charge accumulated in the
capacitor 4 is discharged to the VSS line Lvs faster and by a larger
amount. Accordingly, even when the period P3 is shortened, the gate
voltage Vgs of the driving transistor 2 is sufficiently lowered.
Accordingly, in the period P4, the driving transistor 2 goes into a state
where almost no leakage current occurs between the first-second
electrodes (i.e. between the drain-source). As a result, in the period
P4, charge is less likely to be discharged from the element capacitor 1c
to the VSS line Lvs in pixels that have not yet been subjected to data
writing processing.

[0199]Also, seen from the aspect of control of the potential Vss from the
period P3 to the period P4, a first potential (-β here) is applied
to the VSS line Lvs in a period in which the Vth compensation transistor
3B is placed in the conducting state. Then, with approximately the same
timing with which the Vth compensation transistor 3B changes from the
conducting state to the non-conducting state, the potential Vss is
brought from the first potential to a second potential (0 V here) that is
relatively higher than the first potential.

[0200]By the way, in the driving waveforms shown in FIG. 22, the potential
Vss is raised from -β to 0 V at approximately the same time (time
t4) as the Vth compensation transistor 3B goes into the non-conducting
state when the process moves from the period P3 to the period P4. It is
preferable to consider the following point about the relation between the
timing with which the Vth compensation transistor 3B is placed into the
non-conducting state and the timing with which the potential Vss (i.e.
the potential at the second electrode 2sd of the driving transistor 2) is
raised.

[0201]It is preferable to raise the potential. Vss after the Vth
compensation transistor 3B has been placed in the non-conducting state.
This is because, if some period exists before the Vth compensation
transistor 3B is placed in the non-conducting state after the potential
Vss is raised, charge is accumulated in the capacitor 4 in this period
and it hinders the lowering of the gate voltage Vgs of the driving
transistor 2. However, from the aspect of shortening the period P3, it is
preferable to set as short as possible the period from when the Vth
compensation transistor 3B is placed in the non-conducting state to when
the potential Vss is raised. That is, it is most preferable to set the
same the timing with which the Vth compensation transistor 3B is placed
in the non-conducting state and the timing with which the potential Vss
is raised.

[0202]As to the amount of decrease "β" of the potential Vss, as
described in the second preferred embodiment, when the threshold voltage
Vth=2.2 V, for example, the period P3 can be shortened to 0.2 ms when the
amount of charge accumulated in the capacitor 4 at the end of the period
P3 is lowered by about 0.8 (=1.7-0.9) V. More specifically, the amount of
decrease β of the potential can be set on the basis of the ratio
(capacitance ratio) of the capacitance of the capacitor 4 in the
capacitance of the capacitor 4 and other capacitors.

[0203]As describe above, in the image display apparatus 1C of the third
preferred embodiment, in the period P3, a first potential (-β here)
is applied to the VSS line that is electrically connected to the second
electrode 2sd of the driving transistor 2. Then, with approximately the
same timing with which the Vth compensation transistor 3B changes from
the conducting state to the non-conducting state, the potential Vss is
controlled from the first potential to a second potential (0 V here) that
is relatively higher than the first potential. Also with this
configuration, even when the period P3 is shortened, the driving
transistor 2 substantially goes into the non-conducting state when the
Vth compensation transistor 3B changes from the conducting state to the
non-conducting state. As a result, even when the period P3 is shortened,
almost no differences occur in the amount of decrease of the charge
accumulated in the organic EL device 1 before charge corresponding to the
pixel data signal is accumulated in individual pixels in the period P4.
This makes it possible to lengthen the life of the image display
apparatus while suppressing luminance unevenness and cross-talk on the
screen.

[0204]As compared with the image display apparatus 1A of the first
preferred embodiment, the image display apparatus 1C of the third
preferred embodiment, as well as the image display apparatus 1B of the
second preferred embodiment, is more preferable because this does not
lower the degree of freedom of design, e.g. this does not reduce the
areas for the formation of the driving transistor 2 and the capacitor 4
that are important to adjust the emission luminance of the organic EL
device 1.

[0205]Also, precisely adjusting the potential Vss is easier than precisely
adjusting the overlap in the Vth compensation transistor 3A. Furthermore,
this is preferable also in that the potential Vss can be adjusted after
the pixel circuit 7B has been formed.

[0206]<Modifications>

[0207]The present invention is not limited to the above-described
preferred embodiments, but numerous other modifications and variations
can be devised without departing from the scope of the invention.

[0208]For example, in the image display apparatus 1A of the first
preferred embodiment, the driving transistor 2 and the Vth compensation
transistor 3A are both formed of an n-MISFETTFT, but this is not meant to
be restrictive: the same effects as those of the image display apparatus
1A of the first preferred embodiment can be obtained when they are both
formed of a thin-film transistor that is a kind of field effect
transistor adopting MIS structure of a type (p type) where the carriers
are holes, i.e. p-MISFETTFT.

[0209]In p-MISFETTFT, the positive/negative of the gate voltage for
switching the conducting state and the non-conducting state is reverse to
that in n-MISFETTFT, and therefore the amount of variation of the gate
potential of the driving transistor 2 (i.e. punch-through voltage) has to
be a positive value. However, while (VgL-VgH) on the right side of
Expression (4) is negative in the first preferred embodiment, (VgL-VgH)
on the right side of Expression (4) is replaced by a positive value in
p-MISFETTFT, and therefore the punch-through voltage of the driving
transistor 2 is a positive value.

[0210]Also, in the image display apparatus 1A of the first preferred
embodiment, the structure of the Vth compensation transistor 3A is
adjusted so that the relation of Expression (3) holds, but it is
necessary to variously vary the punch-through voltage of the driving
transistor 2 with circuit design factors, such as the capacitance ratio
of a plurality of capacitors included in the pixel circuit 7A.

[0211]Also, in the first preferred embodiment, the parasitic capacitance
CgsTthA is increased to increase the absolute value of the punch-through
voltage, and as a result the gate voltage (voltage Vgs) of the driving
transistor 2 is increased at the shift from the period P3 to the period.
P4, but this is not meant to be restrictive.

[0212]For example, the absolute value of the punch-through voltage can be
increased by providing a capacitor having one electrode electrically
connected to the sixth electrode 3g of the Vth compensation transistor 3A
and the other electrode electrically connected to the fifth electrode 3sd
of the Vth compensation transistor 3A, i.e. to the third electrode 2g of
the driving transistor 2, whereby the same functions and effects as those
of the first preferred embodiment can be obtained.

[0213]Also, as shown in FIG. 21, in the image display apparatus 1B of the
second preferred embodiment, the potential Vlis in the periods P2 and P3
is set higher than VdH by α and the potential Vlis is lowered to 0
V when the process moves to the period P4, but this is not meant to be
restrictive.

[0214]For example, the same functions and effects as those of the second
preferred embodiment can be obtained when the potential Vlis in the
periods P2 and P3 is set at VdH and the potential Vlis is lowered to
-α that is lower by α than 0V when the process moves to the
period P4 so that the potential Vlis in the period P3 is higher than the
maximum value of the potential Vlis in the period P4. A specific example
thereof will be described below referring to FIG. 23.

[0215]FIG. 23 is a timing chart showing signal waveforms (driving
waveforms) for driving an image display apparatus according to a
modification. FIG. 23 shows potential variation waveforms of the same
kinds as those in FIG. 21.

[0216]In the driving waveforms shown in FIG. 23, the four potentials Vdd,
Vss, Vls1 and Vls2 exhibit the same potential waveforms as those shown in
FIG. 21.

[0217]As to the potential (potential Vlis) applied to the image signal
line Lis, as compared with that shown in FIG. 21, the potential Vlis in
the periods P2 and P3 (time t2 to t4) is set to a value lower by a given
value α (i.e. VdH), and the minimum value and the maximum value of
the potential Vlis in the period P4 (time t4 to t5) are set lower by the
given value a, where the minimum value is -α and the maximum value
is VdH-α. Thus, the absolute values of the potential Vlis in the
periods P2 to P4 differ from those of the second preferred embodiment,
but this is the same as the second preferred embodiment in that the
potential Vlis in the period P3 is set to a higher potential than the
maximum value of the potential Vlis in the period P4.

[0218]When the potential is set in this way, even when the period P3 is
shortened, the gate voltage Vgs of the driving transistor 2 is
sufficiently lowered when the process moves from the period P3 to the
period P4, and the same functions and effects as those of the second
preferred embodiment are obtained.

[0219]Also, in the image display apparatus 1B of the second preferred
embodiment, the driving transistor 2 and the Vth compensation transistor
3B are both formed of an n-MISFETTFT, but this is not meant to be
restrictive; they may both be formed of a thin-film transistor that is a
kind of field effect transistor adopting MIS structure of a type (p type)
where the carriers are holes, i.e. p-MISFETTFT.

[0220]However, when p-MISFETTFT is applied to the driving transistor and
the Vth compensation transistor, the pixel circuit and its driving method
differ.

[0221]Now, first, a pixel circuit in which p-MISFETTFT is applied to the
driving transistor and the Vth compensation transistor, and its basic
driving method, will be described, and then, as in the second preferred
embodiment, a method of appropriately adjusting the potential applied to
the image signal line so that, even when the Vth compensation period is
shortened, the driving transistor goes into the non-conducting state at
the shift to the writing period, will be described.

[0222]Configuration of Pixel Circuit to which p-Type Transistors are
Applied:

[0223]FIG. 24 is a diagram illustrating the circuit configuration of a
pixel circuit 7P using a driving transistor and a Vth compensation
transistor formed of p-MISFETTFT.

[0224]The pixel circuit 7P includes an organic EL device 1, four
transistors Tr1 to Tr4, and two capacitors 4Cc and 4Cs.

[0225]The organic EL device 1 is the same as the organic EL device 1 of
the first to third preferred embodiments, and its anode electrode 1a is
electrically connected to the second electrode R2d of the transistor Tr2
and its cathode electrode 1b is grounded.

[0226]The transistor Tr1 is a driving transistor electrically connected in
series with the organic EL device 1, for adjusting the emission luminance
of the organic EL device 1, and it has an electrode R1d, an electrode
R1s, and a control electrode (gate electrode) R1g. The electrode R1d is
electrically connected to the anode electrode 1a of the organic EL device
1 through the transistor Tr2, the electrode R1s is electrically connected
to a power-supply line (VDD line) Lvd to which a high potential VDD is
applied when the organic EL device 1 emits light, and the gate electrode
Rig is electrically connected to an electrode Cca of the capacitor 4Cc.
The amount of current flowing between the electrode Rid and the electrode
R1s is adjusted by the potential applied to the control electrode Rig,
and a state in which current can flow between the electrode R1d and the
electrode R1s (a conducting state) and a state in which current cannot
flow (a non-conducting state) are realized.

[0227]The transistor Tr2 is electrically connected in series with the
organic EL device 1, and it is a transistor for light emission control
for adjusting the emission timing of the organic EL device 1, and it has
an electrode R2d, an electrode R2s, and a control electrode (gate
electrode) R2g. The electrode R2d is electrically connected to the anode
electrode 1a of the organic EL device 1, the electrode R2s is
electrically connected to the electrode R1d of the transistor Tr1, and
the control electrode R2g is electrically connected to a given
power-supply line (light emission control line) Lec. A state in which
current can flow between the electrode R2d and the electrode R2s (a
conducting state) and a state in which current cannot flow (a
non-conducting state) are realized by the potential applied to the
control electrode R2g from the light emission control line Lec.

[0228]The transistor Tr3 is a Vth compensation transistor for compensating
for the threshold voltage (threshold Vth) of the driving transistor Tr1,
and it has an electrode R3d, an electrode R3s, and a control electrode
(gate electrode) R3g. The electrode R3d is electrically connected to an
interconnection that electrically connects the control electrode R1g of
the driving transistor Tr1 and the capacitor 4Cc, the electrode R3s is
electrically connected to the interconnection that electrically connects
the electrode R1d of the driving transistor Tr1 and the electrode R2s of
the transistor Tr2, and the control electrode R3g is electrically
connected to a given power-supply line (auto-zero line) A state in which
current can flow between the electrode R3d and the electrode R3s (a
conducting state) and a state in which current cannot flow (a
non-conducting state) are realized by the potential applied to the
control electrode R3g from the auto-zero line Lat.

[0229]The transistor Tr4 adjusts whether to effect the potential of the
pixel data signal to the control electrode R1g of the driving transistor
Tr1 and it has an electrode R4d, an electrode R4s, and a control
electrode (gate electrode) R4g. The electrode R4d is electrically
connected to the image signal line Lis, the electrode R4s is electrically
connected to the electrode Ccb of the capacitor 4Cc, and the control
electrode R4g is electrically connected to the scanning signal line Lss.
A state in which current can flow between the electrode R4d and the
electrode R4s (a conducting state) and a state in which current cannot
flow (a non-conducting state) are realized by the potential applied to
the control electrode R4g from the scanning signal line Lss.

[0230]The capacitor 4Cs has a given capacitance Cs, and has an electrode
Csa and an electrode Csb. The electrode Csa is electrically connected to
the interconnection that electrically connects the driving transistor Tr1
and the VDD line Lvd, and the electrode Csb is electrically connected to
the interconnection that electrically connects the control electrode R1g
of the driving transistor Tr1 and the electrode Cca of the capacitor 4Cc,
whereby it is electrically connected to the control electrode R1g, the
electrode Cca, and the electrode R3d of the Vth compensation transistor
Tr3.

[0231]The capacitor 4Cc has a given capacitance Cc, and has an electrode
Cca and an electrode Ccb. The electrode Cca is electrically connected to
the control electrode R1g of the driving transistor Tr1, the electrode
Csb of the capacitor 4Cs, and the electrode R3d of the Vth compensation
transistor Tr3, and the electrode Ccb is electrically connected to the
electrode R4s of the transistor Tr4.

[0232]Method for Driving the Pixel Circuit to which p-Type Transistors are
Applied:

[0233]FIG. 25 is a timing chart illustrating signal waveforms (driving
waveforms) for driving the pixel circuit 7P to cause it to emit light
once. In FIG. 25, the horizontal axis shows time, and the waveforms
sequentially shown from top to bottom include (a) the potential applied
to the VDD line Lvd (potential Vdd), (b) the potential applied to the
auto-zero line Lat (potential Vat), (c) the potential applied to the
light emission control line Lec (potential Vec), (d) the potential
applied to the scanning signal line Lss (potential Vls), and (e) the
potential applied to the image signal line Lis (potential Vlis).

[0234]FIG. 25 shows driving waveforms for causing the organic EL device 1
to emit light once, and the period for one light emission
time-sequentially includes preparatory period Pa (time T1 to T2). Vth
compensation period Pb (time T2 to T3), writing period Pc (time T3 to
T4), and light emission period Pd (time T4 to T5). In FIG. 25, as in
FIGS. 3, 18 and 21-23, the range where the potential Vlis can exist in
the writing period Pc is shown with oblique hatching for the sake of
convenience.

[0235]Now, the operations in the preparatory period Pa (hereinafter also
referred to simply as "period Pa"), the Vth compensation period Pb
(hereinafter also referred to simply as "period Pb"), the writing period
Pc (hereinafter also referred to simply as "period Pc"), and the light
emission period Pd (hereinafter also referred to simply as "period Pd"),
will be described.

[0236]In the period Pa (time T1 to T2), the potential Vdd is set at a
given positive, potential VDD, the potentials Vec and Vls are set at a
given low potential VgL, and the potential Vlis is set at a given
reference potential VdH. The potential Vat is varied from a given high
potential VgH to a given low potential VgL immediately after the process
enters the period Pa. At this time, the four transistors Tr1 to Tr4 all
become conductive, and given charge is accumulated in the capacitors 4Cc
and 4Cs.

[0237]Next, in the period Pb (time T2 to T3), the potential Vdd is kept at
the given positive potential VDD, the potentials Vat and Vls are kept at
the given low potential VgL, and the potential Vlis is kept at the given
reference potential VdH, while the potential Vec is varied from the given
low potential VgH, to a given high potential VgH.

[0238]In the period Pb, first, among the transistors Tr1 to Tr4, the
transistor Tr2 is set in the non-conducting state, whereby positive
charge moves from the electrode R1s of the driving transistor Tr1 to the
electrode R1d and positive charge also moves to the control electrode R1g
of the driving transistor Tr1 through the electrode R3s and the electrode
R3d of the Vth compensation transistor Tr3. Accordingly, the potential at
the control electrode R1g rises. Then, when charge corresponding to the
difference between the reference potential VdH and the threshold Vth
(VdH-Vth) has been accumulated in the capacitor 4Cc, the driving
transistor Tr1 becomes non-conductive.

[0239]Next, in the period Pc (time T3 to T4), the potential Vdd is kept at
the positive given potential. VDU, the potential Vec is kept at the given
high potential VgH, and the potential Vls is kept at the given low
potential VgL, while the potential Vat is set to the given high potential
VgH. The potential Vlis is appropriately set at potential corresponding
to the pixel data signal, and the potential Vls is finally varied to the
given high potential VgH.

[0240]In this period Pc, the Vth compensation transistor Tr1 becomes
non-conductive, and charge corresponding to the potential Vlis, i.e.
charge corresponding to the pixel data signal, is accumulated in the
capacitor 4 Cc, and the transistor Tr4 is made non-conductive, and then
the charge accumulated in the capacitor 4 Cc cannot escape out of the
pixel circuit 7P.

[0241]In the period Pd (time T4 to T5), the potential Vdd is set at the
given positive potential VDD, the potential Vat and Vls are set at the
given high potential VgH, and the potential Vlis is set at the given high
potential VdH, and the potential Vec varies to the given low potential
VgL. At this time, the transistor Tr2 becomes conductive, and the driving
transistor Tr1 is in a conducting state where current corresponding to
the pixel data signal can flow. Accordingly, current corresponding to the
pixel data signal flows from the anode electrode 1a to the cathode
electrode 1b of the organic EL device 1, and the organic EL device 1
emits light with desired luminance.

[0242]Method for Shortening Vth Compensation Period in the Pixel Circuit
to which p-Type Transistors are Applied:

[0243]FIG. 26 is a timing chart illustrating signal waveforms (driving
waveforms) for driving an image display apparatus to which p-type
transistors are applied to the pixel circuits. FIG. 26 shows potential
variation waveforms of the same kinds as those in FIG. 25.

[0244]The driving waveforms shown in FIG. 26 are the same as the driving
waveforms shown in FIG. 25 except in that, in the period Pb (time T2 to
13), the potential Vlis applied to the image signal line Lis is set at a
potential (VdH-α) that is lower by a given potential α than
the reference potential VdH, and so it is lower than the maximum value of
the potential Vlis in the writing period Pc (time 13 to 14).

[0245]Thus, the potential Vlis in the period Pb is adjusted to be lower
than the maximum value of the potential Vlis in the period Pc, whereby
the time that the driving transistor Tr1 takes to become non-conductive
in the period Pb is shortened. Accordingly, even when the Vth
compensation period Pb is shortened, the driving transistor Tr1 goes in a
non-conducting state where almost no leakage current occurs, when the Vth
compensation transistor Tr1 changes from the conducting state to the
non-conducting state. As a result, the same functions and effects as
those of the second preferred embodiment are obtained.

[0246]Also, in the image display apparatus 1C of the third preferred
embodiment, as shown in FIG. 22, the potential Vss applied to the VSS
line Lvs in the periods P2 and P3 is set lower than 0 V by a given value
β, and the potential Vss is raised to 0 V when the process moves to
the period P4, but this it not meant to be restrictive.

[0247]For example, the potential Vss in the periods P2 and P3 may be set
at 0 V, and the Vss may be raised higher than 0 V by a given value β
when the process moves to the period P4. That is, a first potential (0 V
here) is applied to the VSS line Lvs in the period P3, and the potential
Vss is varied from the first potential to a second potential (+β
here) that is relatively higher than the first potential approximately at
the same time as the timing with which the Vth compensation transistor 3B
changes from the conducting state to the non-conducting state. A specific
example thereof will be described referring to FIG. 27.

[0248]FIG. 27 is a timing chart illustrating signal waveforms (driving
waveforms) for driving an image display apparatus according to the
modification. FIG. 27 shows potential variation waveforms of the same
kinds as those in FIG. 22.

[0249]In the driving waveforms shown in FIG. 27, the four potentials Vdd,
Vls1, Vls2 and Vlis are the same potential waveforms as those shown in
FIG. 22.

[0250]As to the potential Vss applied to the VSS line Lvs, as compared
with that shown in FIG. 22, the potential in the periods P2 and P3 (time
t2 to t4) and the period P4 (time t4 to t5) are controlled to be higher
by a given value β. That is, the potential Vss is set at a given
reference potential (0 V here) in the periods P2 and P3, and set at the
given value β in the period P4. Thus, the absolute values of the
potential Vss in the periods P2 to P4 differ from those of the third
preferred embodiment, but this is the same as that of the third preferred
embodiment in that, in the period P3, a first potential (0 V here) is
applied to the VSS line Lvs, and the potential Vss is varied from the
first potential to a second potential (+β here) that is relatively
higher than the first potential at approximately the same time as the
timing with which the Vth compensation transistor 3B changes from the
conducting state to the non-conducting state.

[0251]When the potential is set in this way, the gate voltage Vgs of the
driving transistor 2 is sufficiently lowered when the process moves from
the period P3 to the period P4, and as a result the same functions and
effects as those of the third preferred embodiment are obtained.

[0252]Also, in the image display apparatus 1C of the third preferred
embodiment, the driving transistor 2 and the Vth compensation transistor
3B are both formed of n-MISFETTFT, but this is not meant to be
restrictive; they may both be formed of a thin-film transistor that is a
kind of field effect transistor adopting MIS structure of a type (p type)
where the carriers are holes, i.e. p-MISFETTFT.

[0253]However, when p-MISFETTFT is applied to the driving transistor and
the Vth compensation transistor, the pixel circuit and its driving method
differ. An example of the configuration of the pixel circuit to which
p-type transistors are applied is the pixel circuit 7P described with
FIG. 24.

[0254]Now, a method will be described in which the potential applied to an
electrode that serves as the source of the driving transistor when the
organic EL device emits light is appropriately adjusted, as in the third
preferred embodiment, so that, even when the Vth compensation period is
shortened, the driving transistor substantially goes into the
non-conducting state when the process moves to the writing period.

[0255]FIG. 28 is a timing chart illustrating signal waveforms (driving
waveforms) for driving an image display apparatus to which p-type
transistors are applied to the pixel circuits. FIG. 28 shows potential
variation waveforms of the same kinds as those in FIG. 25.

[0256]The driving waveforms shown in FIG. 28 are the same as the driving
waveforms shown in FIG. 25 except in that the potential Vdd applied to
the VDD line Lvd in the period Pb (time T2 to T3) is set at a potential
higher than the given high potential VDD by a given value. That is, in
the driving waveforms shown in FIG. 28, a first potential (VDD+β
here) is applied to the VDD line Ldd in the period Pb (i.e. the electrode
R1s of the driving transistor Tr1), and the potential Vdd is controlled
to vary from the first potential to a second potential (the given high
potential VDD here) that is relatively lower than the first potential, at
approximately the same time as the timing with which the Vth compensation
transistor Tr3 changes from the conducting state to the non-conducting
state.

[0257]In this way, the potential Vdd in the period Pb is adjusted to be
higher than the potential Vdd in the period Pc, whereby, even when the
period Pb is shortened, the driving transistor Tr1 goes into a
non-conducting state where almost no leakage current occurs, when the Vth
compensation transistor Tr1 changes from the conducting state to the
non-conducting state. As a result, the same functions and effects as
those of the third preferred embodiment are obtained.

[0258]The preferred embodiments described above have illustrated a mobile
phone as an example of an image display apparatus, but this is meant to
be illustrative and not restrictive; for example, the present invention
can be applied to other kinds of image display apparatuses, such as
notebook personal computers and household thin-shaped television
apparatuses, to offer the same effects as those of the preferred
embodiments.

[0259]Also, the preferred embodiments above have illustrated an image
display apparatus using an organic EL display, but the application of the
present invention is not limited to the same; for example, the present
invention can be applied to image display apparatuses having an
arrangement of elements of a type (current-controlled type) in which
emission luminance is adjusted with the amount of current.